WANG Baohong, TANG Keyong, SU Weiming, XU Xianjin, GUO Zhiqiang, LI Hongfei
The unconventional hydrocarbon reservoirs develop in the 2nd Member of Liushagang Formation,Yongan structure,Fushan Sag. Clarifying the microscopic pore structures within its reservoir sandstones is crucial for the development of such hydrocarbon reservoirs. Through various experimental methods,an accurate 2D-3D analysis on the pore structures of the sandstone reservoirs in the 2nd Member of Liushagang Formation is conducted,the main findings are as follows. First, results from thin section examination of rock,field emission scanning electron microscope,MaipSCAN （rock and mineral scanning electron microscope）,cast thin section identification,environmental scanning electron microscope,and high-pressure mercury injection experiments show that the sandstone types of the 2nd Member of Liushagang Formation are mainly lithic sandstone and feldspathic litharenite,with high quartz content. The detrital components are dominated by rock cuttings and quartz,and the heteroatom fillers mainly consist of clay minerals and a small amount of fine silt debris. The pore types in the reservoir space are primarily composed of intergranular residual pores,clastic grain dissolution pores,and grain fractures,with macropores being predominant. Second,the analysis of the constant speed mercury injection experimental data shows that the pore throat types in the reservoirs of the study area are mainly pore-dominated,pore throat co-controlled, and throat-dominated types. Third,the results of the gas adsorption （N2 and CO2） experiments show that the reservoir space is mainly composed of wide,narrow and long slits in the shape of plates,and macropores with pore radii ranging from 50 to 55 nm are mainly developed. Fourth, the distribution and connectivity characteristics of the microscopic pores in the 2nd Member of Liushagang Formation were characterized by 3D reconstruction using FIB-SEM（Focused Ion Beam Scanning Electron Microscopy） and micro-nano CT. The experimental results show that the pore structures of the reservoirs in the study area have good connectivity. Based on the above analysis results,a multi-scale and full pore size joint characterization was conducted,indicating that the pore structure of the sandstones in the study area is dominated by macropores,with underdeveloped microscopic pores and mesopores. By conducting a comprehensive 2D-3D analysis on the pore structures in the 2nd Member of Liushagang Formation,Yongan structure,the microscopic pore structure characteristics of the reservoirs in the study area were deeply dissected,providing more reliable technical support for the later stage of oilfield development in this area.
